Fabry disease: We have extended our basic investigations on enzyme replacement therapy (ERT) and gene therapy (GT) for this hereditary metabolic disorder using the alpha-galactosidase A (alpha-Gal A) knock-out animal model of Fabry disease created by the Developmental and Metabolic Neurology Branch. Intravenous administration of purified alpha-Gal A reduced the toxic accumulations of globotriaosylceramide (Gb3) in many organs of the mice. It restored the prolonged QRS complex to normal, and it reversed the abnormal permeability of kidney glomeruli to albumin. Current experiments are directed to evaluation of ERT on the increased susceptibility of blood vessels to the damaging effects of Gb3. It is anticipated that this information will be of great value in developing treatment strategies for patients with Fabry disease who are particularly susceptible to premature strokes and heart attacks. We have extended our investigations on gene therapy for Fabry disease using the knock-out murine model. Two notable accomplishments occurred in the past year. We found that injection of an adeno-associated virus (AAV) vector containing the alpha-Gal A gene into the hepatic portal vein caused long-term enzymatic and functional correction in multiple organs of the mice. Following the administration of this vector, reduction of Gb3 in the liver, spleen and heart lasted more than 25 weeks. There were no signs of toxicity to AAV. In another investigation, we developed a procedure to preselect stem and progenitor cells that had been transduced with the alpha-Gal A gene. To accomplish this goal, we prepared a biscistronic retroviral vector containing the alpha-Gal A gene as well as the human IL-2Ra chain (huCD25) as the selectable marker. This preselection technique greatly increased the level of multilineage gene-corrected hematopoietic cells in transplanted mice, and it increased the amount of alpha-Gal A activity in the plasma and organs of the transplanted animals. These investigations provide further support of the potential of gene therapy for Fabry disease. Mucolipidosis IV: We reported last year that we discovered the gene that is mutated in patients with this devastating neurogenetic disorder. The product of the gene has been identified as a 580 amino acid protein called mucolipin. We are investigating the function of mucolipin in vitro and in cell cultures. We are preparing antibodies to mucolipin to assist in determining its subcellular localization. Moreover, we are developing models of the disorder in Drosophila and in mice.